The director was recently visited by Horner’s representatives, who stunned him by revealing that the composer had secretly written the score for Fuqua’s forthcoming remake of The Magnificent Seven. The movie is still in production and Horner based his score entirely on a reading of the script.

“He did it all off the script because he wanted to surprise me,” Fuqua told Audie Cornish on America’s National Public Radio, “…and it's just glorious.”

The Magnificent Seven – starring Chris Pratt, Denzel Washington and Ethan Hawke – is not scheduled to be released until January 2017.

Up until the news was announced, it was thought that Horner’s final score would be for The 33, starring Antonio Banderas, which tells the dramatic, true story of the 33 Chilean miners trapped underground for 69 days.

Fuqua described Horner as “an incredible human being”, saying that the composer created the soundtrack for Southpaw at his own expense.

“He called me on a Saturday, after he watched the movie, and I said I don't have any money because it wasn't a big budget movie. And he said to me, I love the movie. I love the father-daughter relationship. Don't worry about the money. I'm just going to do it. And he did it for nothing. He paid his crew out of his own pocket,” said Fuqua.

61-year-old Horner - who won two Oscars for Titanic and also scored Braveheart and Avatar - died last month when his single-engine aircraft crashed in the Los Padres National Forest in California.